This invention relates to a light-tight film cassette containing a roll of photographic film and more particularly to a film cassette in which a film leader of a film roll is fed by rotating a spool having a roll of film wound on it.
In single lens reflex cameras and in compact cameras, a film cassette containing a roll of photographic film strip 35 mm in width is used, as shown in FIG. 34. This type of 35 mm film cassette is designed such that the film strip with one end thereof retained by a spool 1 made of a synthetic resin is wound on the spool 1, the spool 1 having this roll of film rotatably contained in a metallic cassette shell or cassette body 3 and the film leader 2 of the roll of film initially protruding from a film withdrawing slot 3a.
As is known from Japanese Utility Model Publ. No. Sho 41-6297, a plush having long fibers is attached to the inner surface of the film withdrawing slot 3a in order to prevent light from entering the cassette shell 3 through the film withdrawing slot 3a. The film withdrawing slot 3a may be marked, as taught in Japanese Patent Publ No. Sho 43-3416 or Japanese Utility Model Publ. No. Sho 37-32164. Also, with regard to the cassette shell 3, several proposals are made for forming it from a synthetic resin, for example, in order to reduce its weight (Japanese Patent Publ. No. Sho 55-21089).
However, in the case of the above-mentioned film cassette, since the film leader 2 protrudes from the cassette shell 3 even when the film cassette has not yet been used, it sometimes occurs that the users, who may not be very familiar with such products, are at a loss to know how to handle the film leader 2 when putting the film cassette into a camera.
Because of the above, U.S. Pat. Nos. 4,832,275, 4,834,306 and 4,846,418 propose film cassettes in which the film leader is also taken up and kept within the cassette while the film is still unused and the film cassette containing not only the film but also the film leader can be put into a camera in that state. These film cassettes are so designed that the spool disposed within the cassette is rotated by a mechanism on the side of the camera in order to feed the film leader. As the film leader does not protrude from the cassette at all, the operation of loading the film cassette into the camera is easy.
Film cassettes are known, wherein the spool is manually rotated to feed the film leader before the film cassette is put into a camera, as in U.S. Pat. Nos. 4,407,579 and 4,423,943.
In order to feed the film leader smoothly and reliably from the film withdrawing slot by rotating the spool, it is necessary to reduce the resistance applied to the film strip at the time the film is being fed. It is also required, as in the conventional film cassette, that a light-stopping structure be provided so that outside light does not enter the cassette through the film withdrawing slot. If plush is used, as in the prior art, in order to meet this requirement, the resistance applied to the film leader at the time the film is being fed will be great. As a result, the film leader can be bent in the middle of feeding the film and jamming can take place, which stops the feeding of the film. Particularly, in case light is to be excluded merely by providing the plush on the film withdrawing slot, the plush must have a high density of pile yarns and therefore the resistance to movement of the film leader is greatly increased.
In the film cassette described in the above-mentioned U.S. Pat. No. 4,423,943, an opaque sheet is attached to the film leader in order to exclude light and this is wound on the film roll within the cassette in more than one turn. However, such means merely complicates the manufacturing process of the film strip. In addition, waste is increased when the film is developed.
Moreover, in order to prevent the opaque sheet from floating from the outermost periphery of the film roll, the spool is provided with collars projecting from the outer periphery of flanges integrally formed with both end portions of the spool in such a manner as to be opposite to each other, and the collars press against the opaque sheet. In this case, it is required that the cassette and the spool be finished highly accurately. This is also unfavorable in respect of the number of working process steps and the manufacturing cost.